Question

How do metallic character and valency of elements change in a period moving left to right in modern periodic table?

Answer 1

As we move left to right, the nuclear charge on valence shell electron increases. Thus, the tendency to lose electrons decreases. Hence metallic character decreases.

The valency of an element is determined by the number of valence electrons present in the outermost shell of the atom. The valence electrons increases in $s$ and $p$ blocks as moving from left to right. Hence as we move along left to right, valency changes from positive to negative.